Modeling of Helical Gear Carbide Re-Hobbing Process

Carbide re-hobbing is a variation of the gear hobbing process. It is typically used for finishing fully-hardened gear blanks that have been semi-finished, generally by a previous hobbing operation. This paper will discuss a new approach to modeling the carbide re-hobbing process with the goal of improving part quality for a typical pinion. Prior modeling approaches have been based on analytical chip calculation methods. Such approaches, however, limit the geometry of the tool and candidate workpiece to such profiles as would be implemented in the model initially. This new modeling approach involves the use of CAD/CAM/CAE tools to simulate the hobbing process in a virtual 3D environment. As such, the models may now take into account the specific tool geometries, workpiece geometries, setup errors and various cutting conditions with much greater ease. The results of the simulation in predicting cutting forces, part deflection and the resulting profile deviations will be presented. Further, the effect of tool setup error, in particular both synchronous and asynchronous runout, on part quality will be examined in simulation. The simulation results reveal that each type of runout provides a unique signature of profile deviation error for the left and right flanks. The relationship between these setup errors and resulting profile errors will be examined in detail and compared with data from controlled machining tests.